1. Field of the Invention
The invention is based on a connection between a shaft end of a gas exchange valve of an internal combustion engine and a final control element of a valve actuator.
2. Description of the Prior Art
A connection of the type with which this invention is concerned is known from International Patent Disclosure WO 99/66177, with at least two shell-shaped wedge-shaped pieces, surrounding the shaft end and braced on the final control element, whose radially outer circumferential surface extends conically and which are surrounded by at least one conical clamping sleeve whose radially inner circumferential surface extends complimentary to the cone angle of the wedge-shaped pieces, and which is braced on the shaft end axially by a nut screwed onto this end. On the radially inner circumferential surface of the wedge-shaped pieces there is an annular protrusion, which engages an annular groove on the radially outer circumferential surface of the shaft end. The final control element is formed by a differential piston, which can slide up and down inside a cylinder housing of the valve actuator depending on the pressure impingement on its piston end faces pointing away from one another.
Because of the wedging action and the axially prestressed conical clamping sleeve, one radially inner circumferential surface of each of the wedge-shaped pieces rests flush with the shaft end of the gas exchange valve, creating a static frictional engagement between the shaft end and the wedge-shaped pieces that are braced on the differential piston. Rotation of the gas exchange valve about its longitudinal axis, which is favorable for instance for the sake of uniform wear of the valve seat, is then possible only together with a differential piston. Since the pressure chambers, defined by the differential piston and subjected to hydraulic fluid that is under pressure, are sealed off from one another and from the environment by high-pressure seals, relatively high frictional forces must be overcome if the differential piston is to rotate.
The connection according to the invention between a shaft end of a gas exchange valve of an internal combustion engine and a final control element of a valve actuator has the advantage over the prior art that it is effected not by frictional engagement but by positive engagement by means of the protrusions and recesses that engage one another with play, and thus allows rotary motions of the shaft end relative to the final control element. The slightly larger diameter, compared to the shaft end, of the wedge-shaped sleeve formed by the wedge-shaped pieces prevents a frictional engagement, in a manner fixed against relative rotation, between the final control element and the gas exchange valve. Then the final control element need not be rotated along with the gas exchange valve in order to achieve the advantages, such as making valve wear uniform in terms of the circumferential direction or to keep the valve seat free of deposits, advantages known to be associated with regular rotation of the gas exchange valve about its longitudinal axis. Furthermore, the shooting flame of the combustion process then does not always strike the same point of the valve plate, which effectively prevents the development of burned holes. Since the final control element does not rotate along with the gas exchange valve, it can moreover be rotated more easily because the frictional forces are less.
In an especially preferred embodiment, the difference in diameter between the inside diameter of the wedge-shaped sleeve and the outside diameter of the shaft end of the gas exchange valve preferably amounts to a few hundredths of a millimeter. To make it possible to transmit the tensile and compressive forces, the wedge-shaped pieces have at least one annular bead, extending in the circumferential direction and formed on their radially inner, cylindrical circumferential surface, of which annular beads each one engages an associated annular groove embodied in the shaft end, exerted by the final control element on the gas exchange valve, essentially by positive engagement. The annular beads and annular grooves have an essentially semicircular cross section. To avoid a frictionally engaged clamping action between the annular beads and the annular grooves, the inside radius of the annular grooves is slightly greater than the outside radius of the annular beads.
A further refinement provides that a shaft of the gas exchange valve extends from a cylinder head of the engine through an actuator housing of the valve actuator until essentially inside a region of an opening, embodied in an upper wall of the actuator housing. As a result, the valve actuator can be mounted as a completely pre-assembled unit on the cylinder head first, and then the connection of the gas exchange valve and the final control element can be made through the opening or outside the valve actuator housing, which makes it substantially easier to install because of the free accessibility of the opening from above.
Preferably, the final control element of the valve actuator is formed by an actuator sleeve, which with radial spacing surrounds the shaft end of the gas exchange valve and whose free end protrudes some distance out of the opening in the wall of the actuator housing. A radially outer circumferential surface of the conical clamping sleeve is flush with a radially inner, cylindrical circumferential surface of the actuator sleeve, whose inside diameter in the region of the free end of the actuator sleeve is reduced in stages toward the cylinder head by means of a step. Viewed in the radial direction, the conical clamping sleeve is then disposed between the wedge-shaped pieces and the radially inner circumferential surface of the free end of the actuator sleeve, and toward this free end, the outer diameter of the wedge-shaped pieces is conically tapered and the inner diameter of the conical clamping sleeve is conically widened. For bracing the conical clamping sleeve on the actuator sleeve, a clamping body that clamps the conical clamping sleeve to the wedge-shaped pieces is provided, which is braced on the free end of the actuator sleeve by means of a thread or by means of a securing ring that engages a radially inner annular groove of the actuator sleeve, as a result of which the wedge-shaped pieces are axially braced against the step.
Threads or annular grooves for securing rings form notches, however, which can lessen the durability of the connection, which in gas exchange valves is subject to a high number of load changes. Because in a further preferred provision the thread or the securing ring is disposed in a region of the actuator sleeve which is spaced apart preferably axially from the wedge-shaped pieces and conical clamping sleeves that are wedged into one another, the thread or the annular groove for the securing ring is located outside the flow of force and is thus not exposed to any alternating force-introduction stresses. Instead, the thread or the annular groove for the securing ring is subject only to the essentially static prestressing forces that via the wedging action assure that the wedge-shaped pieces hold together. The introduction of force into the gas exchange valve is accordingly accomplished not through the thread or the securing ring but rather through the positive connection made as a result of the intermeshing protrusions and recesses.
In a preferred way, a clamping shim is disposed between the clamping body and an end face, toward the clamping body, of the conical clamping sleeve. As a result, settling of the components that may occur can be compensated for, and the requisite axial prestressing in the connection can be maintained.